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Figure 14.17b
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Table 14.5
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Figure 14.18
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Concept 14.4 Reflexes and SNS Reflex Arcs
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Reflexes somatic reflexes involve contraction of skeletal muscles
autonomic reflexes not consciously perceived responses of smooth muscle, cardiac muscle, and glands reflex arc pathway followed by nerve impulses that produce reflex may be monosynaptic or polysynaptic
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Reflexes fast involuntary, unplanned sequence of actions that occurs in response to a particular stimulus some present from birth some are learned or acquired cranial reflex integration occurs in brain spinal reflex integration occurs in spinal cord SNS reflexes are always excitatory
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SNS Reflex Arc Components
sensory receptor dendrite or associated sensory structure sensory neuron axon and axon terminals integrating center interneuron(s) that relay impulses motor neuron impulse triggered by integrating center effector body part that responds to impulse
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Stretch Reflexes Triggered by tapping on tendons attached to muscles at elbow, wrist, knee, and ankle joints Monosynaptic muscle spindles detect slight stretch muscle spindle generates impulse(s) to sensory neuron to posterior root of spinal nerve sensory neuron synapses with motor neuron in gray matter of spinal cord strong enough impulse triggers AP of motor neuron ACh at NMJ triggers contraction of skeletal muscle
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Figure 14.20
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Stretch Reflexes reciprocal innervation
Monosynaptic reflexes are called ipsilateral reflexes propagate into and out of the same side of spinal cord reflex helps prevent injury by preventing overstretching of muscles reciprocal innervation polysynaptic reflex arc to antagonistic muscles operates at the same time three neurons and two synapses
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Flexor Reflexes Triggered by painful AKA withdrawal reflex
Polysynaptic or intersegmental reflex arc pain-sensitive sensory neuron stimulated impulse propagates into spinal cord sensory neuron activated interneuron and signal sent to several segments several motor neurons activated and motor impulse propagates toward several NMJs ACh released into synaptic cleft causes flexor muscles to contract withdrawing body part from painful stimulus
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Figure 14.21
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Flexor Reflexes reciprocal innervation occurs as in stretch reflex
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Concept ANS Reflexes
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ANS versus SNS SNS ANS produces voluntary movements
in response to consciously perceived sensory input ANS produces involuntary movements in cardiac muscle smooth muscle glands in response to unconscious sensory input
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ANS Reflex Arcs regulates activity of smooth, cardiac muscle, and many glands continual flow of nerve impulses from autonomic sensory neurons in visceral organs and blood vessels propagates into integrating centers of CNS impulses in autonomic motor neurons propagate to various effector tissues can excite or inhibit activities of effector tissues ANS activity is regulated by hypothalamus and brain stem of CNS
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ANS Divisions sympathetic division parasympathetic division
most organs have dual innervation by both sympathetic and parasympathetic divisions transmit opposing nerve impulses enteric division enteric plexuses network of neurons that extend throughout GI tract walls contain sensory neurons interneurons motor neurons
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Figure 14.22a
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Figure 14.22b
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Table 14.6
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Concept 14.6 Anatomy of the ANS
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Components of ANS Preganglionic Neurons Autonomic Ganglia
Postganglionic Neurons Effectors
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Preganglionic Neurons
cell body in CNS sympathetic division in gray matter segments T1-T12, L1 and L2 parasympathetic division in nuclei of four cranial nerves in brain stem in gray matter segments S2-S4 small-diameter myelinated fiber extends to an autonomic ganglion synapses with postganglionic neuron
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Figure 14.23
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Figure 14.24
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Ganglia sympathetic trunk ganglia
Sympathetic ganglia sympathetic trunk ganglia vertical row on either side of vertebral column prevertebral ganglia celiac ganglion superior mesenteric ganglion inferior mesenteric ganglion Parasympathetic ganglia terminal ganglia located close to or actually within wall of visceral organ longer than most axons of sympathetic preganglionic neurons
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Figure 14.25
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Autonomic Plexuses many lie along major arteries
may contain sympathetic ganglia and axons of autonomic sensory neurons often named after associated artery thoracic plexuses cardiac plexus pulmonary plexus abdominal and pelvic plexuses celiac plexus superior and inferior mesenteric plexus hypogastric plexus renal plexus
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Figure 14.25
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Postganglionic Neurons
Sympathetic neurons connect with postganglionic neurons by synapse with first ganglion it reaches may ascent or descent to higher or lower ganglion before synapsing with postganglionic neurons without synapsing it may continue through sympathetic trunk ganglion end at prevertebral ganglion synapse with postganglionic neurons there
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Figure 14.26
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Postganglionic Neurons
Sympathetic effectors some preganglionic sympathetic axons directly innervate adrenal medullae each has many axon collaterals single sympathetic preganglionic fiber may synapse with 20 or more postganglionic neurons example of divergence explains why responses affect almost entire body simultaneously Parasympathetic effectors preganglionic neurons pass to terminal ganglia near or within a visceral effector can be localized to single effector
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Concept 14.7 ANS Signal Transmission
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ANS Signal Transmission
Classification based on neurotransmitter released Cholinergenic neurons release acetylcholine Adrenergenic neurons release norepinephrine
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Cholinergenic neurons
release acetylcholine preganglionic both sympathetic and parasympathetic sympathetic postganglionic that innervate most sweat glands all parasympathetic postganglionic neurons
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Adrenergenic neurons release norepinephrine
most sympathetic postganglionic neurons receptors bind both neurotransmitter norepinephrine and hormone epinephrine four classifications alpha 1, alpha 2, beta 1, and beta 2 alpha 1 and beta 1 are generally excitatory receptors alpha 2 and beta 2 are generally inhibitory receptors
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Figure 14.27a
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Figure 14.27b
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Figure 14.27c
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Table 14.7
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Concept 14.8 Sympathetic and Parasympathetic Responses
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Sympathetic pupil dilation increased heart function
dominates during extreme physical or emotional stress favors activities that can support high production of ATP and high physical activity fight or flight response pupil dilation increased heart function dilation of airways reduced blood flow to viscera increased blood flow to heart, skeletal muscles, liver and adipose tissue increased glycogen and fatty acid breakdown release of glucose from liver inhibition of processes not essential for emergency response
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Parasympathetic salivation lacrimation urination digestion defecation
enhances rest and digest activities favors activities that can support body functions that conserve and restore energy during times of rest and recovery SLUDD salivation lacrimation urination digestion defecation three decreases heart rate diameter of airways diameter of pupils
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Table 14.9 pt 1
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Table 14.9 pt 2
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Table 14.8
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Concept 14.9 ANS Reflex Arcs
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Autonomic Reflexes Components: Receptor Sensory neuron
Integrating center Motor Neuron Effector
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Hypothalamus control and integration center of ANS
receives sensory input regarding visceral function olfaction gustation blood, temperature, osmolarity, and substance concentration emotions from limbic system output via reticular formation to brain stem spinal cord posterior and lateral control sympathetic activities anterior and medial control parasympathetic activities
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End Chapter 14
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